<template>
  <div class="pagination">
    <button :disabled="pageNo == 1" @click="$emit('getPageNo', pageNo - 1)">上一页</button>
    <button v-if="startNumAndEndNum.start > 1" @click="$emit('getPageNo', 1)"  >1</button>
    <button v-if="startNumAndEndNum.start > 2">···</button>

    <button v-for="(num, index) in startEndArr" :key="index" @click="$emit('getPageNo', num)"  :class="{active: pageNo === num}">{{num}}</button>
    
    <button v-if="startNumAndEndNum.end < totalPage - 1">···</button>
    <button v-if="startNumAndEndNum.end < totalPage" @click="$emit('getPageNo', totalPage)"  >{{totalPage}}</button>
    <button :disabled="pageNo == totalPage" @click="$emit('getPageNo', pageNo + 1)">下一页</button>
    
    <button style="margin-left: 30px">共 {{total}} 条</button>
  </div>
</template>

<script>
  export default {
    name: "Pagination",
    props: ['pageNo', 'pageSize', 'total', 'continues'],
    computed:{
      // 总共多少页
      totalPage(){
        // 因为数据多 如果是32.5 那也是33 所以向上取整
        return Math.ceil(this.total / this.pageSize)
      },
      // 计算出连续的页码与起始数字，结束数字
      startNumAndEndNum(){
        const {pageNo, continues, totalPage} = this
        let start= 0, end = 0
        // 正常情况 向下取整
        start = pageNo - parseInt(continues / 2)
        end = pageNo + parseInt(continues / 2)
        // 不正常情况 即 起始 小于1 或结束大于总页数
        if (start < 1) {
          start = 1
          end = continues
        }
        if (end > totalPage) {
          end = totalPage
          start = totalPage - continues + 1 
        }
        if (totalPage < continues) {
          start = 1
          end = totalPage
        }
        return { start, end}
      },
      // 计算起始数字，结束数字 数组
      startEndArr(){
        const {start, end} = this.startNumAndEndNum
        let arr = []
        for (let i = start; i < end + 1; i++){
          arr.push(i)
        }
        return arr
      }
    }
  }
</script>

<style lang="less" scoped>
  .pagination {
    text-align: center;
    button {
      margin: 0 5px;
      background-color: #f4f4f5;
      color: #606266;
      outline: none;
      border-radius: 2px;
      padding: 0 4px;
      vertical-align: top;
      display: inline-block;
      font-size: 13px;
      min-width: 35.5px;
      height: 28px;
      line-height: 28px;
      cursor: pointer;
      box-sizing: border-box;
      text-align: center;
      border: 0;

      &[disabled] {
        color: #c0c4cc;
        cursor: not-allowed;
      }

      &.active {
        cursor: not-allowed;
        background-color: #409eff;
        color: #fff;
      }
    }
  }
</style>
